Question

我正在使用storyboard实现一个简单的应用程序，该应用程序有一个从“普通”视图到tableView的按钮：

enter image description here Bigger picture here.

首先我将导航视图放入故事板并将一个按钮放入RootView（视图“欢迎！”。然后我将一个tableView放入故事板并将两个页面与故事板中的位置 - 按钮链接（ - 直到那时我没有写任何代码）。一切都工作到那时。但后来我为TableView创建了一个LocationsViewController，因为我想用数据填充表格视图单元格。

LocationsViewController.m：

#import "LocationsViewController.h"



@interface LocationsViewController ()
{
    NSArray* locations; //list of cities in our table
}
@end 






@implementation LocationsViewController


- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)didReceiveMemoryWarning
{
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Uncomment the following line to preserve selection between presentations.
    // self.clearsSelectionOnViewWillAppear = NO;

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;

    locations = [NSArray arrayWithObjects:@"New Delhi", @"Durban", @"Islamabad", @"Johannesburg", @"Kathmandu", @"Dhaka", @"Paris", @"Rome", @"Colorado Springs", @"Rio de Janeiro", @"Beijing", @"Canberra", @"Malaga", @"Ottawa", @"Santiago de Chile", nil];

}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
#warning Potentially incomplete method implementation.
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
#warning Incomplete method implementation.
    // Return the number of rows in the section.
    return [locations count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:
                UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }

    // Configure the cell...

    [cell.textLabel setText:[locations objectAtIndex:indexPath.row]];
    return cell;
}

/*
 // Override to support conditional editing of the table view.
 - (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
 {
 // Return NO if you do not want the specified item to be editable.
 return YES;
 }
 */

/*
 // Override to support editing the table view.
 - (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
 {
 if (editingStyle == UITableViewCellEditingStyleDelete) {
 // Delete the row from the data source
 [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
 }   
 else if (editingStyle == UITableViewCellEditingStyleInsert) {
 // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
 }   
 }
 */

/*
 // Override to support rearranging the table view.
 - (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath
 {
 }
 */

/*
 // Override to support conditional rearranging of the table view.
 - (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath
 {
 // Return NO if you do not want the item to be re-orderable.
 return YES;
 }
 */

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Navigation logic may go here. Create and push another view controller.
    /*
     <#DetailViewController#> *detailViewController = [[<#DetailViewController#> alloc] initWithNibName:@"<#Nib name#>" bundle:nil];
     // ...
     // Pass the selected object to the new view controller.
     [self.navigationController pushViewController:detailViewController animated:YES];
     [detailViewController release];
     */
}

@end

LocationsViewController.h：

#import <UIKit/UIKit.h>

@interface LocationsViewController : UITableViewController

@end

由于我将此类声明为TableView的CustomClass，因此按下该按钮不再起作用。在iPhone模拟器上运行应用程序并按下按钮时，应用程序冻结，我收到消息：Program received signal: “EXC_BAD_ACCESS”。

我读到问题是代码中的内存管理错误。我启用了Zombie-Thing并使用控制台消息return [locations count];在[__NSArrayI count]: message sent to deallocated instance 0x6869460点获取了消息。所以它在某个地方解除分配？如何解决问题？任何帮助表示赞赏！

Answer 1

一种可能性是使用属性

in .h

@property (copy, nonatomic) NSArray *locations;

in .m

@synthesize locations;
- (void)viewDidLoad
{
    [super viewDidLoad];
    self.locations = [NSArray arrayWithObjects:@"New Delhi", @"Durban", @"Islamabad", @"Johannesburg", @"Kathmandu", @"Dhaka", @"Paris", @"Rome", @"Colorado Springs", @"Rio de Janeiro", @"Beijing", @"Canberra", @"Malaga", @"Ottawa", @"Santiago de Chile", nil];

}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [self.locations count];
}

Answer 2

第一：

locations = [NSArray arrayWithObjects:@"New Delhi", @"Durban", @"Islamabad", @"Johannesburg", @"Kathmandu", @"Dhaka", @"Paris", @"Rome", @"Colorado Springs", @"Rio de Janeiro", @"Beijing", @"Canberra", @"Malaga", @"Ottawa", @"Santiago de Chile", nil];

[NSArray arrayWithObjects...]会返回一个自动释放的对象，当您将其直接设置为实例变量时，您需要保留它：

locations = [[NSArray arrayWithObjects:@"New Delhi", @"Durban", @"Islamabad", @"Johannesburg", @"Kathmandu", @"Dhaka", @"Paris", @"Rome", @"Colorado Springs", @"Rio de Janeiro", @"Beijing", @"Canberra", @"Malaga", @"Ottawa", @"Santiago de Chile", nil] retain];

注意：使用属性而不是实例变量是一种很好的做法。

第二：

cell = [[UITableViewCell alloc] initWithStyle:
                UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];

根据内存管理规则，alloc init返回一个保留对象，所以你会在这里泄漏。将其更改为：

cell = [[[UITableViewCell alloc] initWithStyle:
                UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];

带有故事板的Xcode 4.2：程序接收信号：“EXC_BAD_ACCESS”

2 个答案: